Method of processing a substrate and a device manufactured by using the method

ABSTRACT

A method of processing a substrate by omitting a photolithographic process is disclosed. The method includes forming at least one layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface, selectively densifying portions of the at least one layer respectively on the upper surface and the lower surface via asymmetric plasma application, and performing an isotropic etching process on the at least one layer. During the isotropic etching process, the portion of the at least one layer formed on the upper surface is separated from the portion of the at least one layer formed on the lower surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Non-Provisional application Ser. No. 15/640,239, filed on Jun. 30, 2017, and entitled “METHOD OF PROCESSING A SUBSTRATE AND A DEVICE MANUFACTURED BY USING THE METHOD,” which claims the benefit of U.S. Provisional Patent Application No. 62/418,502, filed on Nov. 7, 2016 and entitled “THIN FILM DEPOSITION METHOD,” the disclosures of which are incorporated herein in their entireties by reference.

BACKGROUND 1. Field

One or more embodiments relate to methods of processing a substrate via thin film deposition and devices manufactured by using the methods, and more particularly, to a method of processing a substrate by forming an insulation layer (for example, a silicon nitride layer) on a substrate via plasma enhanced atomic layer deposition (PEALD), and a device (for example, a semiconductor device) manufactured by using the method.

2. Description of the Related Art

When a device including a minute circuit pattern formed on a substrate is manufactured, a technique of forming a thin film on a structure having steps is used. In particular, large-scale integrated circuits, such as three-dimensional (3D) semiconductor devices, include a trench structure or a stepped structure, and thus it is required forming a thin film on a selected area of the trench structure or the stepped structure.

SUMMARY

One or more embodiments include selectively depositing a thin film on an area of a structure having steps, without performing a special photolithography process.

One or more embodiments include selectively depositing a thin film on an upper surface and a lower surface of a structure except for a side surface of the structure, wherein the side surface connects the upper surface to the lower surface.

One or more embodiments include selectively depositing a thin film on an upper surface and a lower surface of a stepped structure of a three-dimensional (3D) semiconductor device except for a side surface of the stepped structure.

One or more embodiments include forming a landing pad capable of preventing over-etching of a contact hole formed on a word line (or a sacrificial word line) of a 3D semiconductor device by anisotropic etching.

One or more embodiments include forming the aforementioned landing pad by using a simple process (for example, without a special lithography process and/or by a single etching process).

One or more embodiments include a 3D semiconductor device capable of efficiently preventing signal interference with another word line from occurring in a word line having the aforementioned landing pad.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments.

According to one or more embodiments, a method of processing a substrate includes stacking a stacked structure including a silicon oxide layer and a first silicon nitride layer a plurality of number of times; forming a second silicon nitride layer on the first silicon nitride layer; forming a third silicon nitride layer on the second silicon nitride layer; densifying the third silicon nitride layer; wet-etching at least a portion of a sacrificial word line structure including the first silicon nitride layer, the second silicon nitride layer, and the third silicon nitride layer; forming an interlayer insulation layer on the sacrificial word line structure; removing the sacrificial word line structure; and forming a conductive word line structure corresponding to a space from which the sacrificial word line structure has been removed.

In the wet-etching of at least a portion of the sacrificial word line structure, an etch rate of the third silicon nitride layer may be less than an etch rate of the second silicon nitride layer.

The method may further include etching the stacked structure to form a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface.

In the wet-etching of at least a portion of the sacrificial word line structure, an etch rate of a portion of the third silicon nitride layer on the side surface may be greater than an etch rate of portions of the third silicon nitride layer on the upper and lower surfaces.

The wet-etching of at least a portion of the sacrificial word line structure may include exposing a portion of the second silicon nitride layer formed on the side surface by removing a portion of the third silicon nitride layer formed on the side surface; and exposing a portion of the silicon oxide layer formed on the side surface by removing the second silicon nitride layer.

The exposing of the portion of the second silicon nitride layer and the exposing of the portion of the silicon oxide layer may be performed via a single etch process.

The exposing of the portion of the second silicon nitride layer and the exposing of the portion of the silicon oxide layer may be performed without performing a photolithographic process.

A hydrogen-containing nitrogen gas may be used in the forming of the second silicon nitride layer. Alternatively, a hydrogen-free nitrogen gas may be used in the forming of the third silicon nitride layer.

A flow rate of a hydrogen-containing nitrogen gas used in the forming of the third silicon nitride layer may be less than a flow rate of a hydrogen-containing nitrogen gas used in the forming of the second silicon nitride layer.

A hydrogen content of the third silicon nitride layer may be less than a hydrogen content of the second silicon nitride layer.

The densifying may be performed via an asymmetric plasma process.

A gas including at least one of argon (Ar) and nitrogen may be used during the asymmetric plasma process.

A nitrogen content of the third silicon nitride layer may be greater than a nitrogen content of the second silicon nitride layer.

The conductive word line structure may include a first conductive layer extending toward a channel; a second conductive layer on the first conductive layer; and a third conductive layer on the second conductive layer. The second conductive layer and the third conductive layer may have different sidewall profiles.

The first conductive layer may include a groove, and the groove may be formed adjacent to the second conductive layer.

With respect to one side surface of the second conductive layer and the third conductive layer, one end of the third conductive layer may protrude from a side surface of the second conductive layer. With respect to another side surface of the second conductive layer and the third conductive layer, one end of the second conductive layer may protrude from a side surface of the third conductive layer.

According to one or more embodiments, a method of processing a substrate includes stacking a stacked structure including an insulation layer and a first sacrificial layer a plurality of number of times; forming a second sacrificial layer on the first sacrificial layer; forming a third sacrificial layer on the second sacrificial layer; densifying the third silicon sacrificial layer; etching at least a portion of a sacrificial word line structure including the first sacrificial layer, the second sacrificial layer, and the third sacrificial layer; forming an interlayer insulation layer on the sacrificial word line structure; removing the sacrificial word line structure; and forming a conductive word line structure corresponding to the sacrificial word line structure.

According to one or more embodiments, a method of processing a substrate includes forming a first silicon nitride layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface; forming a second silicon nitride layer on the first silicon nitride layer; selectively densifying the second silicon nitride layer; and performing a wet etching process on the first silicon nitride layer and the second silicon nitride layer, wherein, during the wet etching process, an etch rate of a portion of a nitride layer on the side surface is greater than an etch rate of portions of a nitride layer on the upper and lower surfaces.

According to one or more embodiments, a method of processing a substrate includes forming at least one layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface; selectively densifying, via asymmetric plasma application, portions of the at least one layer respectively on the upper surface and the lower surface except for the side surface; and performing an isotropic etching process on the at least one layer, wherein, during the isotropic etching process, the portion of the at least one layer formed on the upper surface is separated from the portion of the at least one layer formed on the lower surface.

According to one or more embodiments, a semiconductor device includes a substrate; at least one memory cell string extending to protrude from the substrate; a first word line connected to a first memory cell of the memory cell string; and a second word line connected to a second memory cell of the memory cell string, wherein at least one of the first and second word lines includes a first conductive layer extending toward a channel; a second conductive layer on the first conductive layer; and a third conductive layer on the second conductive layer, wherein the second conductive layer and the third conductive layer have different sidewall profiles.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic flowchart of a substrate processing method according to embodiments of the inventive concept;

FIG. 2 is a timing diagram for schematically illustrating a substrate processing method according to embodiments of the inventive concept;

FIG. 3 is a timing diagram for schematically illustrating a substrate processing method according to embodiments of the inventive concept;

FIG. 4 is a timing diagram for schematically illustrating a substrate processing method according to embodiments of the inventive concept;

FIGS. 5 and 6 illustrate results obtained by applying the substrate processing method according to the embodiment of FIG. 2 on a pattern of a stepped structure;

FIGS. 7 and 8 illustrate results obtained by applying the substrate processing method according to the embodiment of FIG. 3 on a pattern of a stepped structure;

FIGS. 9 and 10 illustrate silicon (Si) nitride layers formed via substrate processing methods according to embodiments of the inventive concept;

FIG. 11 is a graph showing variations in the physical property of a silicon nitride layer that contacts plasma, obtained by using a plasma post-treatment using nitrogen (N2) and argon (Ar) on the silicon nitride layer;

FIG. 12 is a schematic diagram of a semiconductor manufacturing apparatus capable of using a semiconductor device manufacturing method according to embodiments of the inventive concept;

FIG. 13 is a table showing a substrate processing method performed by a substrate processing apparatus according to embodiments of the inventive concept;

FIG. 14 is a timing diagram of the substrate processing method of FIG. 13;

FIGS. 15-22 are cross-sectional views for illustrating a substrate processing method according to embodiments of the inventive concept;

FIG. 23 is a circuit diagram of a semiconductor device according to an embodiment of the inventive concept.

FIG. 24 is a cross-sectional view of a semiconductor device manufactured by using a substrate processing method according to embodiments of the inventive concept;

FIGS. 25 and 26 are cross-sectional views illustrating a substrate processing method according to embodiments of the inventive concept and a semiconductor device manufactured by the substrate processing method;

FIG. 27 is a cross-sectional view of a semiconductor device manufactured by using a substrate processing method according to embodiments of the inventive concept;

FIGS. 28-30 are cross-sectional views for explaining the substrate processing method for forming the semiconductor device of FIG. 27 in more detail; and

FIG. 31 is a flowchart of a substrate processing method according to embodiments of the inventive concept.

DETAILED DESCRIPTION

The inventive concept will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the inventive concept are shown.

The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to one of ordinary skill in the art.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the inventive concept.

In the present specification, the term “gas” may include an evaporated solid and/or liquid, and may be a single gas or a mixture of gases. In the present specification, a process gas introduced into a reaction chamber via a shower head may include a precursor gas and an additive gas. The precursor gas and the additive gas may be typically introduced into a reaction space in the form of a mixed gas or may be independently introduced into the reaction space. The precursor gas may be introduced together with a carrier gas, such as an inert gas. The additive gas may include a reactant gas and a dilute gas, such as an inert gas. The reactant gas and the dilute gas may be mixed and introduced into the reaction space, or may be independently introduced into the reaction space. A precursor may include at least one precursor, and a reactant gas may include at least one reactant gas. The precursor is a gas chemisorbed onto a substrate and typically containing metalloid or metal atoms that form a major structure of a matrix of a dielectric film, and the reactant gas for deposition is a gas that reacts with the precursor chemisorbed onto the substrate when the gas is excited to form an atomic layer or a monolayer onto the substrate. “Chemisorption” refers to chemically-saturated adsorption. A gas other than the process gas, namely, a gas introduced, other than via the shower head, may be used to seal the reaction space. The gas includes a seal gas, such as an inert gas. According to some embodiments, a “film” refers to a layer that continuously extends in a direction perpendicular to a thickness direction without pin holes in order to cover the entire area of a target or a partial surface related to the target, or a layer that simply covers the target or the partial surface related with the target. According to some embodiments, a “layer” refers to a structure having a certain thickness formed on a surface, a film-type layer, or a non-film structure. A film or layer may be a single discontinuous film or layer having certain characteristics or may include multiple films or layers. A boundary between adjacent films or layers may be clear or unclear and may be set based on physical characteristics, chemical characteristics, and/or other types of characteristics, forming processes or a forming sequence, and/or functions or purposes of adjacent films or layers.

In the present specification, a phrase “containing a Si—N bond” may be characterized by a Si—N bond or Si—N bonds which may have a main frame substantially formed by a Si—N bond or Si—N bonds and/or a substituent substantially formed by an Si—N bond or Si—N bonds. A silicon nitride layer may be a dielectric layer containing a Si—N bond, and may include a silicon nitride layer (SiN) and a silicon oxynitride layer (SiON).

In the present specification, the term “the same material” should be interpreted as including the same main constituent. For example, when a first layer and a second layer are both silicon nitride layers and are formed of the same material, the first layer may be selected from the group consisting of Si2N, SiN, Si3N4, and Si2N3 and the second layer may also be selected from the same group, but in detail, a film material of the second layer may be different from that of the first layer.

In addition, in the present specification, according as an executable range may be determined based on a routine operation, two parameters may constitute an executable range, and an indicated range may include or exclude end points. In addition, values of some indicated parameters (regardless of whether or not the values are indicated by “about”) may refer to accurate values or approximate values, and may include equivalents thereof. According to some embodiments, the values of some indicated parameters may refer to an average value, a center value, a representative value, a multi value, and the like.

In the present specification, when conditions and/or structures are not specified, one of ordinary skill in the art may easily provide these conditions and/or structures as an issue of a customary experiment. In all disclosed embodiments, a component used in one embodiment includes components disclosed explicitly, necessarily, or intrinsically herein for intended purposes, and thus may be replaced by any of components equivalent to the component. Furthermore, the present invention is equally applicable to devices and methods.

Embodiments of the inventive concept are described herein with reference to schematic illustrations of embodiments of the inventive concept. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the inventive concept should not be construed as being limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing.

FIG. 1 is a schematic flowchart of a substrate processing method according to embodiments of the inventive concept.

Referring to FIG. 1, in operation S 1, a first insulation layer is formed on a stepped structure. The first insulation layer may be formed by atomic layer deposition (ALD), in particular, by plasma enhanced ALD (PEALD).

The first insulation layer may be formed to have a relatively low density (and accordingly to have a high etch rate). To this end, during the ALD for the first insulation layer, a gas including hydrogen (for example, a hydrogen-containing nitrogen gas) may be used. By performing deposition by using a gas including hydrogen, more Si—H bonds may be formed in the first insulation layer, and accordingly a wet etch rate (WER) of the first insulation layer in a subsequent etching process may increase.

Thereafter, in operation S2, a second insulation layer is formed on the first insulation layer. The second insulation layer may be the same as the first insulation layer. For example, when the first insulation layer is a silicon oxide layer, the second insulation layer may be a silicon oxide layer. When the first insulation layer is a silicon oxynitride layer, the second insulation layer may be a silicon oxynitride layer. A process of forming the first insulation layer and a process for forming the second insulation layer may be performed in-situ in the same reactor or may be performed ex-situ in different reactors.

The second insulation layer may be formed to have a relatively high density (and accordingly to have a low etch rate). The second insulation layer may be formed by ALD or PEALD, during which a gas not including hydrogen (for example, a hydrogen-free nitrogen gas) may be used. According to a selective embodiment, a hydrogen content of the gas used during the process for forming the second insulation layer may be less than that of the gas used during the process for forming the first insulation layer.

By performing a deposition process of the second insulation layer by using a gas including no hydrogen or having a less hydrogen content, fewer Si—H bonds may be formed in the second insulation layer, and accordingly a WER of the second insulation layer in a subsequent etching process may be lower than that of the first insulation layer.

Thereafter, in operation S3, a plasma post-treatment may be performed. The plasma post-treatment may be performed using capacitively coupled plasma (CCP) that is excited by applying radio frequency (RF) power to at least one of two electrodes. According to a selective embodiment, together with the processes of respectively forming the first insulation layer and the second insulation layer, the plasma post-treatment may be performed in-situ in the same reactor, or may be performed ex-situ in different reactors.

The plasma post-treatment may be performed using an asymmetric plasma process, and the second insulation layer may be selectively densified by the asymmetric plasma process. The asymmetric plasma process includes a process of applying plasma such that the plasma has directivity, and thus selective densification with respect to a thin film deposited on a stepped structure may be achieved due to the directivity of the applied plasma.

For example, plasma may be applied to a structure having an upper surface, a lower surface, and a side surface connecting the upper surface to the lower surface, in a direction parallel to the side surface. In this case, collision with active species such as radicals and/or charged particles generally occurs on the upper surface and the lower surface of the stepped structure due to the directivity of the applied plasma, whereas relatively less collision with active species such as radicals and/or charged particles occurs on the side surface of the structure.

According to a selective embodiment, during the asymmetric plasma process, a gas including argon (Ar) may be used. During the asymmetric plasma process, the Ar gas may be activated, and thus active species may be generated. Due to directivity of the active species, portions of the second insulation layer respectively formed on the upper surface and the lower surface of the stepped structure may be selectively densified. Such densification may occur due to ion bombardment by the active species.

According to another selective embodiment, during the asymmetric plasma process, a gas including a constituent of the second insulation layer may be used. For example, when the second insulation layer is a silicon nitride layer, during the asymmetric plasma process, a gas including a constituent of the second insulation layer (for example, nitrogen) may be activated and thus active species may be generated. Due to directivity of nitrogen plasma, the nitrogen plasma may be applied to the portions of the second insulation layer (silicon nitride layer) respectively formed on the upper surface and the lower surface of the stepped structure. Accordingly, a nitrogen component, which is a constituent of the second insulation layer, may increase, and thus a silicon nitride layer enriched with nitrogen may be formed.

According to another selective embodiment, during the asymmetric plasma process, a gas not including hydrogen (or a gas not including a hydrogen component) may be used. In other words, the gas may not include a hydrogen gas, or hydrogen may not be included in the constituents of the gas. For example, during a plasma post-treatment on a silicon nitride layer, a hydrogen-free nitrogen gas (for example, a nitrogen (N2) gas) may be used instead of ammonia (NH3).

After the plasma post-treatment, wet etching may be performed, in operation S4. In the wet etching, the first insulation layer and the second insulation layer may be removed. This removal may be conducted partially from a selected area. In other words, when the first insulation layer and the second insulation layer are formed on a structure having an upper surface, a lower surface, and a side surface connecting the upper surface to the lower surface, portions of the first insulation layer and the second insulation layer formed on the side surface may be removed via wet etching, but portions of the first insulation layer and the second insulation layer respectively formed on the upper surface and the lower surface may remain during wet etching.

During the wet etching, a semiconductor device is dipped into a liquid etchant and a surface of the substrate is etched by a chemical reaction. Because the wet etching is isotropic etching, the isotropic etching may not greatly affect selective etching of the first insulation layer and the second insulation layer. Rather, according to the inventive concept, while the first insulation layer and the second insulation layer are being formed on the stepped structure, portions of the insulation layer formed on the upper and lower surfaces of the stepped structure are rendered to have a different physical property from the portion of the insulation layer formed on the sidewall of the stepped structure, and thus selective etching may be achieved during a subsequent etching process. In other words, steps performed before the etching process serve as factors that control the process conditions of a subsequent wet etching step.

The factors and/or elements that control the process condition include at least one of the following steps.

Step of forming the first insulation layer: at least one of forming a lower insulation layer having a high WER, removing an insulation layer formed on a sidewall of a lower support structure via etching of the lower support structure without complete etching of an upper insulation layer, and/or supplying a gas including a hydrogen component.

Step of forming the second insulation layer: at least one of forming the upper insulation layer having a low WER, preventing an insulation layer from being etched from a selected area of the lower support structure (e.g., a top and a bottom) during wet etching, and/or supplying a gas including no hydrogen component or including a low hydrogen component.

Step of applying plasma: at least one of densification of the second insulation layer (and the first insulation layer), directivity of plasma, ion bombardment of active species (not including hydrogen), and/or applying gas plasma having an insulation layer constituent.

As such, at least one of the aforementioned steps serves as a factor for controlling a subsequent etching process, whereby selective etching of the first insulation layer and the second insulation layer may be achieved.

FIG. 2 is a timing diagram for schematically illustrating a substrate processing method according to embodiments of the inventive concept.

Referring to FIG. 2, a method of forming a SiN film via PEALD is disclosed as a deposition method capable of controlling a WER of the SiN film.

According to the present embodiment, a PEALD SiN film deposition step is divided into two steps, and then, a plasma post-treatment is conducted.

To this end, the SiN thin film is formed via a first step, a second step, and a third step. The first and second steps are included in the PEALD SiN thin film deposition step, and the third step is the plasma post-treatment.

The first step is depositing the SiN thin film, which is a first insulation layer, on a substrate. As shown in FIG. 2, a SiN film having a desired thickness is formed by repeating a basic PEALD cycle several times (for example, m cycle). The basic PEALD cycle includes source feeding (t0 to t1)/purging (t1 to t2)/reactant feeding (t2 to t4)/RF plasma (t3 to t4)/purging (t4 to t5).

During the first step, DCS (SiH2Cl2; dichlorosilane) may be used as a Si source, and ammonia (NH3), which is a nitrogen source including hydrogen, may be used as a reactant. However, the Si source and the reactant used in the present invention are not limited thereto. For example, the Si source may be, instead of DCS, TSA, (SiH3)3N; DSO, (SiH3)2; DSMA, (SiH3)2NMe; DSEA, (SiH3)2NEt; DSIPA, (SiH3)2N(iPr); DSTBA, (SiH3)2N(tBu); DEAS, SiH3NEt2; DIPAS, SiH3N(iPr)2; DTBAS, SiH3N(tBu)2; BDEAS, SiH2(NEt2)2; BDMAS, SiH2(NMe2)2; BTBAS, SiH2(NHtBu)2; BITS, SiH2(NHSiMe3)2; TEOS, Si(OEt)4; SiCl4; HCD, Si2Cl6; 3DMAS, SiH(N(Me)2)3; BEMAS, Si H2[N(Et)(Me)]2; AHEAD, Si2 (NHEt)6; TEAS, Si(NHEt)4; Si3H8, or the like. Alternatively, a combination of these sources may be used as the Si source. The reactant in the present invention may be a nitrogen gas including hydrogen, and NH4+ or the like instead of NH3 may be used as the reactant.

A mixed gas of Ar and N2 is used as a purge gas and may be continuously supplied into a reaction space by varying a flow rate thereof according to the steps. The N2 gas serves as a reactive purge gas in the present embodiment. During a period (t3 to t4) in which a reactive gas is activated due to supply of plasma, the N2 gas may also be activated and may serve as a constituent of the SiN film.

During the first step, a Si3N4 film having a stoichiometric composition may be formed. During the first step, nitrogen (N2), which is a reactive purge gas, may be further supplied in addition to the reactive gas of NH3, in order to generate sufficient nitrogen radical. The N2 gas may be supplied together with an Ar purge gas.

According to a selective embodiment, the first step may include a reactant pre-flow step (t2 to t3). By performing the reactant pre-flow step, the reactive gas may be uniformly distributed in the reaction space before plasma is supplied into the reaction space, and thus a distribution of the reactive gas within the reaction space may become uniform in a plasma supply step, leading to a more stable process.

After the first step, during the second step, a SiN thin film, which is a second insulation layer, may be formed on the first insulation layer. As shown in FIG. 2, a SiN film having a desired thickness is formed by repeating a PEALD cycle several times (for example, n times). The PEALD cycle includes source feeding (t5 to t6)/purging (t6 to t7)/reactant feeding (t7 to t9)/RF plasma (t8 to t9)/purging (t9 to t10).

The first step and the second step may be common in that an insulation layer containing a Si—N bond is formed by ALD, but may be different in detailed process parameters. For example, a flow rate or supply time of the reactive gas during the period (t2 to t4) in which the reactant is supplied in the first step may be different from that of the reactive gas during the period (t7 to t9) in which the reactant is supplied in the second step.

Moreover, the source and the reactant used in the second step may be different from those used in the first step. In more detail, during the second step, a material containing a relatively low amount of hydrogen may be used as the Si source. According to a selective embodiment, a material not including hydrogen may be used as the Si source. A nitrogen source containing a low amount of hydrogen or not containing hydrogen may be used as the reactant. Moreover, the content of nitrogen in the reactant used in the second step may be higher than that used in the first step.

Due to such differences between process parameters of the first and second steps, a first silicon nitride layer and a second silicon nitride layer formed on the top of the first silicon nitride layer may have different densities and different WERs. For example, when the flow rate of the reactive gas of NH3 in the first step is greater than that of NH3 in the second step, the SiN film formed in the first step is less dense than that formed in the second step (for example, having a smaller number of Si—N bonds than the SiN film formed in the second step) and accordingly has a higher WER than the SiN film formed in the second step, due to a larger amount of hydrogen component included in the first silicon nitride layer.

After the first step and the second step are repeated several times to form a SiN film having a desired thickness, a plasma post-treatment using a mixed gas of Ar and N2 is performed in the third step. During one cycle of the third step, the mixed gas of Ar and N2 may be supplied (t10 to t11), and then plasma may be applied (t11 to t12). This cycle may be repeated a plurality of number of times (for example, x times). During the third step, an ion bombardment effect may be obtained due to Ar ions within the plasma, and wet etching resistivity of the SiN film (especially its upper part) may be further improved due to the nitrogen component.

In the third step, as a hydrogen gas degrades wet etching resistivity of an insulation layer, hydrogen or a gas including hydrogen is not supplied and a mixed gas of Ar and N2 is supplied.

The ion bombardment effect due to Ar activated without supplying H* radical increases wet etching resistivity of a target film. In this case, Ar ions have directivity (straightness), and thus an ion bombardment effect is large on an upper surface and a lower surface of a stepped structure and an ion bombardment effect is small on a vertical sidewall or inclined sidewall of the stepped structure that connects the upper surface to the lower surface. Thus, a film formed on the sidewall has less density than and a higher WER than a film formed on the upper or lower surface.

Nitrogen (N2) increases densification of a thin film (see FIG. 11). Similar to Ar, N2 plasma or N2 ions also has directivity. Thus, a relatively large number of N2 ions are injected into portions of a silicon nitride layer formed on the upper and lower surfaces and thus an N-rich silicon nitride layer is formed, whereas a relatively small number of N2 ions are injected into a portion of the silicon nitride layer formed on the sidewall. Accordingly, due to the plasma post-treatment, nitrogen contents of the portions of the second silicon nitride layer formed on the upper and lower surfaces are greater than a nitrogen content of the portion of the second silicon nitride layer formed on the sidewall.

As such, according to embodiments of the inventive concept, by performing the plasma post-treatment, ion bombardment of Ar activated without H*radical supply and/or densification of a thin film by nitrogen may be achieved, and accordingly resistivity with respect to subsequent etching of the thin film may be selectively controlled.

According to a selective embodiment, during the plasma post-treatment, an ion bombardment effect by Ar ions within the plasma and/or densification of the thin film by N2 ions are achieved, and, independently, during the first silicon nitride layer forming step and the second silicon nitride layer forming step, the density and the WER of the SiN film may be controlled by varying plasma supply conditions (plasma power, a plasma frequency, an Ar/N2 flow rate, and the like). Moreover, because a hydrogen component is one of major factors that affect resistivity with respect to wet etching of a film, the WER of the silicon nitride layer may be controlled by adjusting a hydrogen content of the Si source and/or the N2 reactant (for example, by adjusting a NH3 flow rate) in the step of forming the first silicon nitride layer.

According to a selective embodiment, by varying the plasma supply conditions (plasma power, a plasma frequency, an NH3 flow rate, an Ar/N2 flow rate, and the like) of the first and second steps, the densities and WERs of the SiN films respectively formed in the first step and the second step may be controlled. In other words, the plasma application steps (t3 to t4) and (t8 to t9) of different conditions may be performed during PEALD so that the SiN film formed in the second step is denser and has higher wet etching resistivity than the SiN film formed in the first step. The SiN film formed in the second step is formed on top of the SiN film formed in the first step.

FIG. 3 is a timing diagram for schematically illustrating a substrate processing method according to embodiments of the inventive concept. The substrate processing method of FIG. 3 may be a modification of the substrate processing method according to the above-described embodiments. Duplicated descriptions between the embodiments will now be omitted.

Referring to FIG. 3, formation of a SiN thin film on a stepped structure may be achieved via a PEALD SiN thin film deposition step, a plasma post-treatment step, and a subsequent wet etching step. In the embodiments of FIG. 2, the PEALD SiN thin film deposition step is divided into two steps, and different process parameters are applied in the two steps. However, in the embodiments of FIG. 3, the PEALD SiN thin film deposition step is a single step.

The PEALD SiN thin film deposition step may be performed by repeating a basic PEALD cycle several times (for example, m times). The basic PEALD cycle includes source feeding (t0 to t1)/purging (t1 to t2)/reactant feeding (t2 to t4)/RF plasma (t3 to t4)/purging (t4 to t5). Various materials or a combination thereof may be used as a source material and a reactant. As described above, resistivity with respect to subsequent wet etching of a formed film may vary due to hydrogen contents in the source material and the reactant.

Thereafter, a plasma post-treatment step is performed (t5 to t7). As described above, during one cycle of the plasma post-treatment step, a mixed gas of Ar and N2 may be supplied (t5 to t6), and then plasma may be applied (t6 to t7) in an environment of the mixed gas of Ar and N2. This cycle may be repeated a plurality of number of times (for example, n times).

Process conditions in the plasma post-treatment step may be different from those during application of RF plasma in the PEALD SiN thin film deposition step. For example, flow rates of Ar and N2 and a mixing ratio therebetween during the plasma post-treatment step may be different from those during the RF Plasma application in the PEALD SiN thin film deposition step. The intensity of RF power supplied during the plasma post-treatment step may be different from that supplied during the RF Plasma application in the PEALD SiN thin film deposition step.

As described above, the plasma post-treatment step may be performed via an asymmetric plasma process (e.g., plasma with directivity), and accordingly, a feature of a silicon nitride layer formed on the stepped structure may be controlled differently according to positions of the stepped structure.

FIG. 4 is a timing diagram for schematically illustrating a substrate processing method according to embodiments of the inventive concept. The substrate processing method of FIG. 4 may be a modification of the substrate processing method according to the above-described embodiments. Duplicated descriptions between the embodiments will now be omitted.

Referring to FIG. 4, formation of a SiN thin film on a stepped structure is achieved via a first PEALD SiN thin film deposition step, a second PEALD SiN thin film deposition step, and a subsequent wet etching step. In the embodiments of FIG. 2, a PEALD SiN thin film deposition step divided into two steps is performed and then a plasma post-treatment is performed. However, in the embodiments of FIG. 4, without a plasma post-treatment, the subsequent wet etching step is performed after a PEALD SiN thin film deposition step divided into two steps.

The first PEALD SiN thin film deposition step may be performed by repeating a basic PEALD cycle several times (for example, m times). The basic PEALD cycle includes source feeding (t0 to t1)/purging (t1 to t2)/reactant feeding (t2 to t4)/RF plasma (t3 to t4)/purging (t4 to t5). Thereafter, the second PEALD SiN thin film deposition step may be performed by repeating a basic PEALD cycle several times (for example, n times). The basic PEALD cycle includes source feeding (t5 to t6)/purging (t6 to t7)/reactant feeding (t7 to t9)/RF plasma (t8 to t9)/purging (t9 to t10).

As described above, by using different source materials and different reactants in the first PEALD SiN thin film deposition step and the second PEALD SiN thin film deposition step, resistivity with respect to subsequent wet etching of a deposited film may be changed.

According to a selective embodiment, by controlling the directivity of the RF plasma application performed in the second PEALD SiN thin film deposition step, a feature of second silicon nitride layer formed on the stepped structure may be controlled to vary according to positions of the stepped structure.

FIGS. 5 and 6 illustrate results obtained by applying the substrate processing method according to the embodiment of FIG. 2 on a pattern of a stepped structure. FIG. 5 illustrates silicon nitride layers before wet etching is performed, and FIG. 6 illustrates silicon nitride layers after wet etching is performed.

Referring to FIGS. 2 and 5, the first PEALD SiN thin film deposition step (first step) and the second PEALD SiN thin film deposition step (second step) are performed so that a first silicon nitride layer 2 and a second silicon nitride layer 3 are sequentially formed on a pattern 1 having a stepped structure. Each of the first and second silicon nitride layers 2 and 3 may have a thickness of 50 to 200 Å. According to a selective embodiment, the first silicon nitride layer 2 may have a thickness of 100 to 130 Å, and the second silicon nitride layer 3 may have a thickness of 120 to 150 Å.

According to an embodiment, flow rates of NH3 supplied in the two steps of the PEALD SiN thin film deposition step may have a relative range of 3:1 to 50:1. In this case, less NH3 is supplied to the second silicon nitride layer 3 than to the first silicon nitride layer 2, and thus resistivity with respect to wet etching of the second silicon nitride layer 3 increases compared with the first silicon nitride layer 2. Thus, a WER or a wet etch rate ratio (WERR) of the second silicon nitride layer 3 is less than that of the first silicon nitride layer 2.

Thereafter, a plasma post-treatment (third step) is conducted. Due to the straightness of plasma and N2 ions, a property of a film may vary according to positions of the stepped structure. In other words, ion bombardment is concentrated on an upper surface U and a lower surface L of the stepped structure and ion bombardment is relatively small on a portion of the silicon nitride layer formed on a side surface S of the stepped structure, and thus a property of the silicon nitride layer differs according to positions of the stepped structure. Thus, during the subsequent wet etching step, the portion of the silicon nitride layer on the side surface S may be first etched. Consequently, portions of the silicon nitride layer on the upper surface U and the lower surface L remain, and thus selective wet etching may be achieved.

FIG. 6 illustrates a silicon nitride layer formed on the upper surface U and the lower surface L of the stepped structure after wet etching. Because properties of the silicon nitride layer formed on the upper surface U and the lower surface L became different from a property of the silicon nitride layer formed on the sidewall S due to processes (for example, a plasma post-treatment) before wet etching, the silicon nitride layer formed on the sidewall S may be preferentially etched.

In more detail, the portion of the second silicon nitride layer formed on the sidewall S may be preferentially etched during wet etching, and accordingly, the first silicon nitride layer may be exposed. In this case, the second silicon nitride layer may remain on the upper surface U and the lower surface L. When the portion of the first silicon nitride layer on the sidewall S is exposed, the first silicon nitride layer on the sidewall S may be more quickly etched than the second silicon nitride layer on the upper surface U and the lower surface L because the first silicon nitride layer has a higher etch rate than the second silicon nitride layer. Accordingly, the first silicon nitride layer and the second nitride layer formed on the sidewall S are more quickly removed than a second nitride layer formed on the upper surface U and the lower surface L.

Thus, according to embodiments of the inventive concept, wet etching selectivity between an upper/lower layer and a sidewall layer on a pattern of a stepped structure may be maximized.

FIGS. 7 and 8 illustrate results obtained by applying the substrate processing method according to the embodiment of FIG. 3 on a pattern of a stepped structure. FIG. 7 illustrates a silicon nitride layer before wet etching is performed, and FIG. 8 illustrates a silicon nitride layer after wet etching is performed.

Referring to FIGS. 3 and 7, the PEALD SiN thin film deposition step is performed, and thus a silicon nitride layer is formed on the pattern 1 having a stepped structure. The silicon nitride layer may have a thickness of 100 to 400 Å.

Thereafter, a plasma post-treatment is conducted. As described above, due to the straightness of plasma and nitride ions, a property of the silicon nitride layer may vary according to positions of the stepped structure.

FIG. 8 illustrates a silicon nitride layer formed on the upper surface U and the lower surface L of the stepped structure after wet etching. Because properties of the silicon nitride layer formed on the upper surface U and the lower surface L became different from a property of the silicon nitride layer formed on the sidewall S due to processes (for example, a plasma post-treatment) before wet etching, the silicon nitride layer formed on the sidewall S may be preferentially etched.

Assuming that a thickness of the silicon nitride layer formed via a two-step PEALD process (i.e., a first silicon nitride layer and a second silicon nitride layer) in FIG. 6 is equal to that of the silicon nitride layer of FIG. 8, the silicon nitride layer of FIG. 6 formed via the two-step PEALD process is thicker than the silicon nitride layer of FIG. 8 after wet etching is performed. It will be understood that the thickness difference is generated because a second silicon nitride layer having large wet etching resistivity is formed on top of a first silicon nitride layer formed on the upper surface U and the lower surface L.

FIGS. 9 and 10 illustrate silicon nitride layers formed via substrate processing methods according to embodiments of the inventive concept. FIG. 9 illustrates a silicon nitride layer obtained via wet etching after two-step silicon nitride layer deposition and a plasma post-treatment, and FIG. 10 illustrates a silicon nitride layer obtained via wet etching after single-step silicon nitride layer deposition and a plasma post-treatment.

Via wet etching, the silicon nitride layer formed on a sidewall of a stepped structure is removed, whereas the silicon nitride layer formed on an upper surface and a lower surface of the stepped structure remain. A thickness of a remaining silicon nitride layer in FIG. 9 is about 230 Å on average, whereas a thickness of a remaining silicon nitride layer in FIG. 10 is about 150 Å on average. Consequently, when a SiN film having high wet etch resistivity is deposited on a top of a thin film that contacts plasma via a two-step PEALD process, wet etch selectivity between upper/lower surfaces and a sidewall of a stepped structure may be maximized.

This improvement of wet etch selectivity based on a two-step silicon nitride layer is related to a hydrogen content and a nitrogen content of an upper silicon nitride layer preferentially exposed to an etchant during subsequent wet etching. In other words, etch resistivity may not only be reinforced by the above-described plasma post-treatment, but also etch resistivity of the upper silicon nitride layer may be reinforced by forming silicon nitride layers having different properties (for example, a low hydrogen content and/or a high nitrogen content) via the two-step PEALD process.

FIG. 11 is a graph showing variations in the property of a silicon nitride layer that contacts plasma, by applying a plasma post-treatment using nitrogen and Ar to the silicon nitride layer. In the graph of FIG. 11, the x axis indicates the number of cycles of a third step (plasma post-treatment). In the graph of FIG. 11, the y axis on the left side indicates a Si/N ratio and a WERR of a silicon nitride layer according to the number of cycle. In the graph of FIG. 11, the y axis on the right side indicates a hydrogen content of the silicon nitride layer according to the number of cycle.

Referring to FIG. 11, as a plasma post-treatment is conducted over a plurality of cycles, the Si/N ratio of the silicon nitride layer decreases. This means that a nitrogen content of the silicon nitride layer increases due to nitrogen (i.e., nitrogen plasma (ions)) supplied during the plasma post-treatment. In other words, a nitrogen gas may increase a nitrogen component of an upper silicon nitride layer (for example, Si2N→SiN→Si3N4→Si2N3), and accordingly a WER of the upper silicon nitride layer may decrease.

As the plasma post-treatment is conducted over a plurality of cycles, the hydrogen content of the silicon nitride layer decreases. This means that a percentage of a hydrogen component contained in the silicon nitride layer decreases by applying Ar and nitrogen (i.e., Ar/N2 plasma (ions)) supplied during the plasma post-treatment to the silicon nitride layer. In other words, the relative portion of hydrogen in the film decreases

Due to these factors, wet etch resistivity of the silicon nitride layer after the plasma post-treatment increases. Referring to FIG. 11, a WERR of the silicon nitride layer before the plasma post-treatment is 1.46, whereas a WERR of the silicon nitride layer after 120 cycles are performed during the plasma post-treatment is 0.58 and a WERR of the silicon nitride layer after 400 cycles are performed during the plasma post-treatment is 0.22.

Therefore, according to embodiments of the inventive concept, by forming an upper silicon insulation layer having a certain thickness and performing a plasma post-treatment for a certain number of cycles, a WERR of a silicon insulation layer may be controlled, and accordingly, the silicon insulation layer formed on a stepped structure may be selectively etched during subsequent isotropic etching.

FIG. 12 is a schematic diagram of a semiconductor manufacturing apparatus to which a semiconductor device manufacturing method according to embodiments of the inventive concept is applicable.

Referring to FIG. 12, a substrate processing apparatus may be implemented to vertically supply a gas toward a substrate by using a gas spraying unit. For example, the substrate processing apparatus of FIG. 12 may be a PEALD apparatus for forming a silicon nitride layer. A substrate processing apparatus according to embodiments of the inventive concept will now be described on the premise that DCS (Dichlorosilane; Si2H2Cl2) is used as an Si source and ammonia (NH3) is used as a nitrogen source.

The PEALD apparatus may include a reactor 10, a gas spraying unit 20, an exhaust unit 30, a DCS supply line 40, an Ar supply line 50, an N2 supply line 60, an NH3 supply line 70, a DCS bypass line 80, an NH3 bypass line 90, a first supply line 100, and a second supply line 110. The PEALD apparatus may further include first through seventh valves (V1 to V7) for controlling gas flows via the lines. Functions of the first through seventh valves V1 through V7 are as follows.

The first valve V1 controls connection between the DCS supply line 40 and a first supply line 100.

The second valve V2 controls connection between the DCS supply line 40 and the DCS bypass line 80.

The third valve V3 controls connection between the Ar supply line 50 and the first supply line 100.

The fourth valve V4 controls connection between the NH3 supply line 70 and the second supply line 110.

The fifth valve V5 controls connection between the NH3 supply line 70 and the NH3 bypass line 90.

The sixth valve V6 controls connection between the Ar supply line 50 and the second supply line 110.

The seventh valve V7 controls connection between the Ar supply line 50 and the N2 supply line 60.

The reactor 10 is a space for performing silicon nitride thin film deposition on a Si substrate (not shown), and may be an enclosed space. To this end, the reactor 10 may be isolated from the outside of the reactor 10 by using an enclosing unit, such as a seal gas and/or an O-ring, and may be typically maintained at a pressure of an air pressure or less. A substrate support unit or a susceptor (not shown) on which the Si substrate is placed may be disposed in the reactor 10, and a gate valve (not shown) that enables substrate access may be provided on a lateral side of the reactor 10. In this case, the gate value may open only when the substrate is loaded or unloaded, and may maintain a closed state during a process.

The gas spraying unit 20 may be configured to uniformly supply DCS, NH3, Ar, and N2 supplied via the first supply line 100 and the second supply line 110 onto the Si substrate. For example, the gas spraying unit 20 may be a shower head. According to a selective embodiment, the gas spraying unit 20 may be connected to an RF plasma generator, and accordingly, a PEALD process may be conducted. According to another embodiment, the gas spraying unit 20 may serve as a plasma electrode.

A source/reactive gas having passed through the reactor 10 may be exhausted via the exhaust unit 30. The exhaust unit 30 may include at least one exhaust line (not shown) connected to the outside.

The substrate processing apparatus may further bypass lines. For example, as in the present embodiment, the PEALD apparatus may include the DCS bypass line 80 and the NH3 bypass line 90. In this case, DCS and NH3 are alternately supplied into the reactor 10 and a PEALD process is conducted in this state. When DCS is supplied into the reactor 10, NH3 may be exhausted to the exhaust unit 30 via the NH3 bypass line 90. When NH3 is supplied into the reactor 10, DCS may be exhausted to the exhaust unit 30 via the DCS bypass line 80. In other words, the source/reactive gases may maintain a continuous flow state while being alternately supplied to the reactor and the bypass line according to a switching method, and thus pressures within the gas supply line and the reactor may be maintained uniformly. Consequently, process stability may be maintained.

FIG. 13 is a table showing a method of processing a substrate by using a substrate processing apparatus according to embodiments of the inventive concept (for example, the substrate processing apparatus of FIG. 12). FIG. 14 is a timing diagram of the substrate processing method of FIG. 13. The substrate processing method of FIG. 13 may be a modification of the substrate processing method according to the above-described embodiments. Duplicated descriptions between the embodiments will be omitted.

Referring to FIGS. 12-14, in a step of forming a first silicon nitride layer (i.e., a first step), DCS as a Si source, Ar, N2, and NH3 are supplied. The DCS, the Ar, the N2, and the NH3 may be supplied via the DCS supply line 40, the Ar supply line 50, the N2 supply line 60, and the NH3 supply line 70, respectively, and may be supplied, for example, at 200 sccm to 600 sccm, 1000 sccm to 2000 sccm, 100 sccm to 300 sccm, and 1000 sccm to 2000 sccm, respectively.

During one cycle of the first step, via switching of the first through seventh valves V1 through V7, source feeding (t0 to t1), source purging (t1 to t2), reactant pre-flow (t2 to t3), and reactant flow and plasma application (t3 to t4), and purging (t4 to t5) may be performed for 0.3 seconds to 0.7 seconds, for 0.1 seconds to 0.3 seconds, for 0.1 seconds to 0.5 seconds, for 0.5 seconds to 0.9 seconds, and for 0.1 seconds to 0.3 seconds, respectively. By performing this cycle (t0 to t5) a plurality of number of times, the first silicon nitride layer may be formed. During the first step, a pressure in the reactor may be maintained at 3 Torr to 5 Torr, a temperature may be maintained at 450° C., and RF power supplied during reactant flow and plasma application (t3 to t4) may be 50 W to 150 W.

Thereafter, a step of forming a second silicon nitride layer on the first silicon nitride layer (i.e., a second step) is performed. During the second step, DCS, as a Si source, Ar, N2, and NH3 are supplied. The DCS, the Ar, the N2, and the NH3 may be supplied via the DCS supply line 40, the Ar supply line 50, the N supply line 60, and the NH3 supply line 70, respectively, and may be supplied, for example, at 800 sccm to 1200 sccm, 2500 sccm to 3500 sccm, 400 sccm to 600 sccm, and 40 sccm to 80 sccm, respectively.

During one cycle of the second step, via switching of the first through seventh valves V1 through V7, source feeding (t5 to t6), source purging (t6 to t7), and reactant flow and plasma application (t7 to t8), and purging (t8 to t9) may be performed for 0.3 seconds to 0.7 seconds, for 0.3 seconds to 0.5 seconds, for 1 seconds to 3 seconds, and for 0.1 seconds to 0.3 seconds, respectively. By performing this cycle (t5 to t9) a plurality of number of times, the second silicon nitride layer may be formed. During the second step, a pressure in the reactor 10 may be maintained at 3 Torr to 5 Torr, a temperature may be maintained at 450° C., and RF power supplied during reactant flow and plasma application (t7 to t8) may be 200 W to 400 W.

When first process parameters of the first step are compared with second process parameters of the second step, a supply amount of NH3 having a hydrogen component in the second step is less than that of NH3 in the first step, a supply amount of N2 not having a hydrogen component in the second step is greater than that of N2 in the first step, and, in the second step, reactant pre-flow is omitted, and instead, larger power of plasma is applied for a longer period of time than in the first step. These second parameters different from the first process parameters aim to form a silicon nitride layer having high wet etching resistivity on a top of a stepped structure (i.e., on a location preferentially exposed to a wet etchant) as described above.

Thereafter, a plasma post-treatment (i.e., a third step) is conducted. During the third step, Ar and N2 are supplied, and NH3 having a hydrogen component is not supplied. Ar and N2 may be supplied via the Ar supply line 50 and the N supply line 60, respectively. For example, Ar and N2 may be supplied at 2500 sccm to 3500 sccm and 400 sccm to 600 sccm, respectively.

During one cycle of the third step, via switching of the first through seventh valves V1 through V7, purging (t9 to t10) and reactant flow and plasma application (t10 to t11) may be performed for 0.1 seconds to 0.5 seconds and for 0.1 seconds to 0.5 seconds, respectively. By performing this cycle (t9 to t11) a plurality of number of times, the second silicon nitride layer may be selectively densified according to points of a stepped structure. During the third step, a pressure in the reactor 10 may be maintained at 3 Torr to 5 Torr, a temperature may be maintained at 450° C., and RF power supplied during reactant flow and plasma application (t10 to t11) may be 200 W to 400 W.

FIGS. 15-22 are cross-sectional views for illustrating a substrate processing method according to embodiments of the inventive concept. The substrate processing method of FIGS. 15-22 may be a modification of the substrate processing method according to the above-described embodiments. Duplicated descriptions between the embodiments will now be omitted.

Referring to FIG. 15, insulation layers 210 a, 210 b, 210 c, and 210 d (hereinafter, referred to as an insulation layer 210) and first sacrificial layers 220 a, 220 b, 220 c, and 220 d (hereinafter, referred to as a first sacrificial layer 220) are alternately stacked on a substrate 200 a plurality of number of times to thereby form a stacked structure. For example, the insulation layer 210 may be a silicon oxide layer, and the sacrificial layer 220 may be a silicon nitride layer. However, embodiments are not limited thereto, and the insulation layer 210 and the first sacrificial layer 220 may be formed of materials having different etch selectivities.

Thereafter, a process is performed, for etching the insulation layer 210 and the first sacrificial layer 220 to form channel holes and forming at least some of the components of a memory cell string MCS of FIG. 23 within the channel holes. The memory cell string may include components, such as a channel, a gate conductive layer, and a gate insulation layer.

A process for forming the components of the memory cell string may be performed by directly forming at least some of the channel, the gate conductive layer, and the gate insulation layer, or may be performed by forming a sacrificial layer in a channel hole so that the channel, the gate conductive layer, and the gate insulation layer may be formed in a subsequent process, or may be performed via a combination of these two methods.

Referring to FIG. 16, a stepped structure is formed by etching one end of the stacked structure including the insulation layer 210 and the first sacrificial layer 220. The stepped structure may be formed via, for example, reactive ion etching and resist sliming.

The stepped structure has an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface. For example, the stepped structure may include at least one step ST, and a step ST may have an upper surface U on the first sacrificial layer 220 b, a lower surface L on the first sacrificial layer 220 a, and a side surface S that connects the upper surface U to the lower surface L.

Referring to FIG. 17, at least one layer is formed on the stepped structure. The layer may be, for example, an insulation layer. The insulation layer may be formed via the two-step PEALD process according to the above-described embodiments. In this case, a second sacrificial layer 230 may be formed on the first sacrificial layer 220, and a third sacrificial layer 240 may be formed on the second sacrificial layer 230.

The second sacrificial layer 230 and the third sacrificial layer 240 may be formed of the same material as the material used to form the first sacrificial layer 220. For example, when the insulation layer 210 is a silicon oxide layer and the first sacrificial layer 220 is a silicon nitride layer, the second sacrificial layer 230 and the third sacrificial layer 240 may also be silicon nitride layers (i.e., a second silicon nitride layer and a third silicon nitride layer).

As described above, the second sacrificial layer 230 and the third sacrificial layer 240 may be formed to have different properties. For example, when the first sacrificial layer 220, the second sacrificial layer 230, and the third sacrificial layer 240 are formed of a first silicon nitride layer, a second silicon nitride layer, and a third silicon nitride layer, respectively, a hydrogen-containing nitrogen gas may be used during forming the second silicon nitride layer, which is on bottom of the third silicon nitride layer, and a hydrogen-free nitrogen gas may be used during forming the third silicon nitride layer, which is on top of the second silicon nitride layer.

According to a selective embodiment, the flow rate of a hydrogen-containing nitrogen gas used during forming the third silicon nitride layer may be less than that of a hydrogen-containing nitrogen gas used during forming the second silicon nitride layer. A Si precursor may be selected such that the hydrogen content of the third silicon nitride layer is less than that of the second silicon nitride layer.

According to an additional embodiment, the third silicon nitride layer may be formed such that the nitrogen content of the third silicon nitride layer may be greater than that of the second silicon nitride layer. This is based on the principle (see FIG. 11) that, as a Si/N ratio decreases, wet etching resistivity increases. To this end, during forming the third silicon nitride layer, more nitrogen may be supplied than NH3 (see FIG. 13).

Thereafter, a step of densifying the third sacrificial layer 240 (for example, the third silicon nitride layer), that is, a plasma post-treatment, is conducted. The plasma post-treatment may be performed using an inert gas, such as Ar, and/or a gas having a constituent of a sacrificial layer (for example, nitrogen when the third sacrificial layer 240 is a silicon nitride layer).

The plasma post-treatment (i.e., a densifying step) may be conducted using an asymmetric plasma process. Due to directivity of plasma ions by the asymmetric plasma process, only portions of the third sacrificial layer 240 (for example, the third silicon nitride layer) respectively formed on the upper surface U and the lower surface L of the step ST may be densified. Accordingly, during subsequent isotropic etching, selective etching of a sacrificial layer on a stepped structure may be achieved.

Referring to FIG. 18, at least a portion of a sacrificial word line structure including the first sacrificial layer 220, the second sacrificial layer 230, and the third sacrificial layer 240 (for example, the first silicon nitride layer, the second silicon nitride layer, and the third silicon nitride layer) is etched. This etching may be isotropic etching. In more detail, the etching may be performed using a wet etching process, and by using, for example, phosphoric acid or fluoric acid.

During the etching, an etch rate of a portion of a sacrificial layer (for example, the third silicon nitride layer) on the side surface S of a step may be greater than that of portions of the sacrificial layer on the upper surface U and the lower surface L of the step. Accordingly, only the portion of the sacrificial layer on the side surface S may be removed, and the portions of the sacrificial layer on the upper surface U and the lower surface L may remain.

During the etching, the etch rate of the third sacrificial layer 240 on top of the second sacrificial layer 230 (for example, the third silicon nitride layer on top of the second silicon nitride layer) may be less than that of the second sacrificial layer 230 (for example, the second silicon nitride layer). A difference between etch rates of upper and lower layers is caused for several reasons. For example, the etch rate difference may be caused because, during forming the second sacrificial layer 230 on the bottom of the third sacrificial layer 240, a relatively large amount of a hydrogen-containing reactant is supplied and thus the second sacrificial layer 230 has a low density, or because etching resistivity of the third sacrificial layer 240 on top of the second sacrificial layer 230 was relatively improved by the step of densifying the third sacrificial layer 240.

According to a selective embodiment, the etching step may be conducted according to the following mechanisms.

In a first mechanism, the portion of the third sacrificial layer 240 (for example, the third silicon nitride layer) formed on the side surface S of a step is preferentially removed. Accordingly, a portion of the second sacrificial layer 230 (for example, the second silicon nitride layer) formed on the side surface S of the step is exposed to an etching material. However, portions of the third sacrificial layer 240 respectively formed on the upper and lower surfaces U and L of the step are not removed, and thus portions of the second sacrificial layer 230 respectively formed on the upper and lower surfaces U and L are not exposed to the etching material (see FIG. 28).

In a second mechanism, the portion of the second sacrificial layer 230 on the side surface S exposed to the etching material is removed. At this time, the portion of the third sacrificial layer 240 remaining on the side surface S may also be removed. Accordingly, portions of the insulation layer 210 (for example, the silicon oxide layer) and the first sacrificial layer 220 (for example, the first silicon nitride layer) formed on the side surface S may be exposed (see FIG. 29).

In a third mechanism, the portions of the insulation layer 210 and the first sacrificial layer 220 on the side surface S exposed to the etching material are removed. At this time, portions of the second sacrificial layer 230 and the third sacrificial layer 240 remaining on the side surface S may be partially removed (see FIG. 30). Because the second sacrificial layer 230 and the third sacrificial layer 240 have different properties, sidewall profiles of the second sacrificial layer 230 and the third sacrificial layer 240 after wet etching may be different from each other (see FIG. 30).

In more detail, because the third sacrificial layer 240 was formed via a PEALD process and/or a plasma post-treatment having a smaller amount of hydrogen-containing gas, the third sacrificial layer 240 has higher wet etching resistivity than the second sacrificial layer 230. Accordingly, the third sacrificial layer 240 may have a sidewall that protrudes beyond the sidewall of the second sacrificial layer 230.

The above-described first through third mechanisms are conducted during a single etch process. In other words, in a substrate processing method according to embodiments of the inventive concept, a thin film may be selectively formed on an area of a stepped structure via deposition without an additional photolithographic process. Furthermore, by performing the subsequent wet etching process, adequate isolation between metal word line structures created by the sacrificial word line structure may be achieved (see FIG. 27). This is technically important in that isolation between conductive word line structures may be achieved via control of wet process parameters without a minute process, such as photolithography.

Referring to FIG. 19, an interlayer insulation layer 250 is formed on a structure obtained after etching. The interlayer insulation layer 250 may be formed of the same material as a material used to form the insulation layer 210 located between sacrificial layers of the stepped structure. For example, a sacrificial layer of the stepped structure may be a silicon nitride layer, the insulation layer 210 of the stepped structure may be a silicon oxide layer, and the interlayer insulation layer 250 may be a silicon oxide layer.

Referring to FIG. 20, via contacts 260 connected to at least a portion of the sacrificial layer are formed starting from the upper surface of the interlayer insulation layer 250, via patterning. According to a selective embodiment, the via contacts 260 may be formed after the sacrificial layer is etched and thus a conductive word line structure is formed.

Referring to FIG. 21, the sacrificial layer is etched such that a channel (not shown), the insulation layer 210, the interlayer insulation layer 250, and the via contacts 260 are exposed. Accordingly, the sacrificial word line structure including the first sacrificial layer 220 of FIG. 20, the second sacrificial layer 230 of FIG. 20, and the third sacrificial layer 240 of FIG. 20 may be removed. According to a selective embodiment, during the sacrificial layer etching step, a second sacrificial layer 230′ of FIG. 20 and a third sacrificial layer 240′ of FIG. 20 formed on the substrate 200 may be simultaneously removed, and accordingly, a portion of an upper surface of the substrate 200 may be exposed.

Referring to FIG. 22, a conductive word line structure WL is formed in an exposed space. The conductive word line structure WL may be formed to correspond to a space from which the sacrificial word line structure has been removed. The conductive word line structure WL may be tungsten, and may include a material selected from various materials having conductivity, such as copper and polysilicon, or a combination thereof.

The thus-formed conductive word line structure WL may include the following components:

a first conductive layer C1 (corresponding to the first sacrificial layer 220 of FIG. 20) extending toward the channel;

a second conductive layer C2 (corresponding to the second sacrificial layer 230 of FIG. 20) located on one end of the first conductive layer C1; and

a third conductive layer C3 (corresponding to the third sacrificial layer 240 of FIG. 20) on the second conductive layer C2.

In other words, the first conductive layer C1, the second conductive layer C2, and the third conductive layer C3 included in the conductive word line structure WL are based on layers formed via different processes (i.e., sacrificial layers).

As described above, according to embodiments of the inventive concept, the second sacrificial layer and the third sacrificial layer have different properties. Accordingly, after the wet etching of FIG. 19 is performed, the second sacrificial layer and the third sacrificial layer may have different sidewall profiles, and accordingly, the second conductive layer C2 and the third conductive layer C3 of the conductive word line structure WL of FIG. 22 may also have different sidewall profiles.

FIG. 23 is a circuit diagram of a semiconductor device according to an embodiment of the inventive concept. The semiconductor device may be formed according to the substrate processing method according to the aforementioned embodiments. Duplicated descriptions between the embodiments will now be omitted.

Referring to FIG. 23, a semiconductor memory device may include the substrate 200, the memory cell string MCS, a first word line WL1, and a second word line WL2.

The memory cell string MCS may protrude and extend from the substrate 200. The memory cell string MCS may include a plurality of memory cells. Although four memory cells are illustrated in FIG. 23, more or less memory cells may be implemented within a single memory cell string MCS, as necessary.

The first word line WL1 may be connected to a first memory cell MC1. For example, the first word line WL1 may extend toward a channel of the first memory cell MC1. Similarly, the second word line WL2 may be connected to a second memory cell MC2 and may extend toward a channel of the second memory cell MC2.

At least one of the first word line WL1 and the second word line WL2 may include the word line structure formed via the step of FIG. 22. Accordingly, at least one of the first word line WL1 and the second word line WL2 may include the first conductive layer C1, the second conductive layer C2 on the first conductive layer C1, and the third conductive layer C3 on the second conductive layer C2, which extend toward a channel, and the second conductive layer C2 and the third conductive layer C3 may have different sidewall profiles.

FIG. 24 is a cross-sectional view of a semiconductor device manufactured by using a substrate processing method according to embodiments of the inventive concept. The semiconductor device of FIG. 24 may be a modification of the semiconductor device according to the above-described embodiments. Duplicated descriptions between the embodiments will now be omitted.

The semiconductor device of FIG. 24 is different from the semiconductor device of FIG. 22 in that the second sacrificial layer 230′ and the third sacrificial layer 240′ remain on the substrate 200. This difference may be generated because, during the sacrificial layer etching step of FIG. 21, the second sacrificial layer 230′ and the third sacrificial layer 240′ formed on the substrate 200 were not exposed to an etchant. In this case, the second sacrificial layer 230′ and the third sacrificial layer 240′ on the substrate 200 may become a structure remaining in a final product of a semiconductor device.

FIGS. 25 and 26 are cross-sectional views illustrating a substrate processing method according to embodiments of the inventive concept and a semiconductor device manufactured by using the substrate processing method. The substrate processing method and the semiconductor device of FIGS. 25 and 26 may be a modification of the substrate processing method and the semiconductor device according to the above-described embodiments. Duplicated descriptions between the embodiments will now be omitted.

Referring to FIG. 25, the insulation layer 210 may be a silicon oxide layer, and a sacrificial word line structure including the first sacrificial layer 220, the second sacrificial layer 230, and the third sacrificial layer 240 may be formed of a silicon nitride layer (i.e., the first silicon nitride layer, the second silicon nitride layer, and the third silicon nitride layer). To separate a sacrificial word line structure located on top of a stepped structure ST from a sacrificial word line structure located on bottom of the stepped structure ST, a step of etching the silicon nitride layer by using phosphoric acid may be performed.

During the phosphoric acid etching, due to different properties (for example, different WERRs) of the first silicon nitride layer, the second silicon nitride layer, and the third silicon nitride layer, the sacrificial word line structure may have an overhang structure.

For example, with respect to one side surface of the second silicon nitride layer and the third silicon nitride layer (on a right sidewall surface of the stepped structure ST of FIG. 25), one end of the third silicon nitride layer may protrude from the side surface of the second silicon nitride layer. With respect to the other side surface of the second silicon nitride layer and the third silicon nitride layer (toward a left sidewall surface of the stepped structure ST of FIG. 25), one end of the second silicon nitride layer may protrude from the side surface of the third silicon nitride layer.

Thereafter, as shown in FIG. 26, a step of forming a conductive word line structure WL may be performed. The conductive word line structure WL may be formed to correspond to a space from which the sacrificial word line structure has been removed. Accordingly, with respect to one side surface of the second conductive layer C2 and the third conductive layer C3 (right surface of FIG. 25), one end of the third conductive layer C3 may protrude from the side surface of the second conductive layer C2. With respect to the other side surface of the second conductive layer C2 and the third conductive layer C3 (left surface of FIG. 25), one end of the second conductive layer C2 may protrude from the side surface of the third conductive layer C3. Accordingly, as shown in FIG. 26, a portion of the conductive word line structure WL may have a parallelogram-like overhang structure.

FIG. 27 is a cross-sectional view of a semiconductor device manufactured by a substrate processing method according to embodiments of the inventive concept. FIGS. 28-30 are cross-sectional views for explaining the substrate processing method for forming the semiconductor device of FIG. 27 in more detail. The semiconductor device of FIG. 27 may be a modification of the semiconductor device according to the above-described embodiments. Duplicated descriptions between the embodiments will now be omitted.

Referring to FIG. 27, during a wet etching step, a sacrificial word line structure located on top of a stepped structure may be separated from a sacrificial word line structure located on bottom of the stepped structure. The wet etching step is a single wet step. As described above, during the single wet step, the first mechanism (FIG. 28), the second mechanism (FIG. 29), and the third mechanism (FIG. 30) are conducted.

By performing the wet etching step, a groove G may be formed on a portion of the first sacrificial layer 220 adjacent to the side surface of a stepped structure (i.e., between the insulation layer 210 and the second sacrificial layer 230). Accordingly, when a conductive word line structure is formed later to correspond to a space from which the sacrificial word line structure has been removed, a first conductive layer (corresponding to the first sacrificial layer 220) of the conductive word line structure may include a groove, which may be formed adjacent to a second conductive layer (corresponding to the second sacrificial layer 230) of the conductive word line structure.

FIG. 31 is a flowchart of a substrate processing method according to embodiments of the inventive concept. A semiconductor device of FIG. 31 may be a modification of the semiconductor device according to the above-described embodiments. Duplicated descriptions between the embodiments will be omitted.

Referring to FIG. 31, in operation S310, at least one layer is formed on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface. The at least one layer may include an arbitrary material, such as an insulative material or a conductive material.

Via subsequent asymmetric plasma application, the plasma having directivity, portions of the at least one layer respectively on the upper surface and the lower surface except for the side surface are selectively densified, in operation S320. During the asymmetric plasma application, particles, such as arbitrary types of active species, radicals, and ions, may be incident upon a substrate in a direction substantially perpendicular to the substrate. According to another embodiment, during the asymmetric plasma application, particles, such as arbitrary types of active species, radicals, and ions, may be incident in a direction substantially parallel to the side surface of the stepped structure. As described above, via the asymmetric plasma application, densification of the at least one layer may be performed differently according to positions of the stepped structure.

Thereafter, an isotropic etching process is performed on the at least one layer, in operation S330. Due to a difference between film materials of layers according to different positions of the stepped structure via the asymmetric plasma application, the layer formed on the upper surface and the layer formed on the lower surface may be separated from each other during the isotropic etching process.

As such, in the substrate processing method according to embodiments of the inventive concept, a thin film may be selectively formed on an upper surface and a lower surface of a stepped structure via a wet etching. Furthermore, the selectively-formed thin films may be sufficiently spaced apart from each other during the wet etching step. Thus, a photolithographic process for selectively forming thin films on the upper surface and the lower surface of the stepped structure and for spacing the thin films apart from each other by a certain interval may be omitted.

To clearly understand the inventive concept, the shape of each region in the accompanying drawings needs to be understood as an example. It should be noted that the shape of each region may vary. Like numbers refer to like elements throughout the specification.

While the inventive concept has been particularly shown and described with reference to the exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims. 

What is claimed is:
 1. A method of processing a substrate, the method comprising: forming a first layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface; forming a second layer on the first layer, the second layer being formed of the same material as a material for the first layer; and performing an isotropic etching process on the first layer and the second layer, wherein, during the isotropic etching process, an etch rate of a portion of the second layer on the side surface is greater than an etch rate of portions of the second layer on the upper and lower surfaces, and wherein the method further comprises selectively densifying the second layer.
 2. The method of claim 1, wherein the densifying is performed via an asymmetric plasma application.
 3. The method of claim 1, wherein the second layer is selectively densified through a post-plasma treatment after the forming the second layer.
 4. The method of claim 1, wherein the second layer is selectively densified during the forming the second layer.
 5. The method of claim 4, wherein a plasma is applied during the forming the second layer, and wherein a directivity of the plasma is controlled to control a feature of the second layer according to positions of the stepped structure.
 6. A method of processing a substrate, the method comprising: forming a first layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface; forming a second layer on the first layer, the second layer being formed of the same material as a material for the first layer; and performing an isotropic etching process on the first layer and the second layer, wherein, during the isotropic etching process, an etch rate of a portion of the second layer on the side surface is greater than an etch rate of portions of the second layer on the upper and lower surfaces, and wherein a flow rate of a hydrogen-containing gas used in the forming of the second layer is less than a flow rate of a hydrogen-containing gas used in the forming of the first layer.
 7. A method of processing a substrate, the method comprising: forming a first layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface; forming a second layer on the first layer, the second layer being formed of the same material as a material for the first layer; and performing an isotropic etching process on the first layer and the second layer, wherein, during the isotropic etching process, an etch rate of a portion of the second layer on the side surface is greater than an etch rate of portions of the second layer on the upper and lower surfaces, and wherein a hydrogen content of the second layer is less than a hydrogen content of the first layer.
 8. A method of processing a substrate, the method comprising: forming at least one layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface, wherein portions of the at least one layer respectively on the upper surface and the lower surface except for the side surface are selectively densified via an asymmetric plasma application.
 9. The method of claim 8, further comprising: performing an isotropic etching process on the at least one layer, wherein, during the isotropic etching process, the portion of the at least one layer formed on the upper surface is separated from the portion of the at least one layer formed on the lower surface.
 10. The method of claim 8, wherein the at least one layer is formed through a PEALD process using the asymmetric plasma application.
 11. The method of claim 10, wherein the PEALD process a cycle including source feeding, purging, reactant feeding, RF plasma, and purging, and wherein the asymmetric plasma application is achieved by the RF plasma.
 12. A method of processing a substrate, the method comprising: a first SiN thin film deposition step to form a first silicon nitride layer on a stepped structure having an upper surface, a lower surface, and a side surface that connects the upper surface to the lower surface; a second PEALD SiN thin film deposition step to form a second nitride layer on the first silicon nitride layer; and a wet etching step after the second PEALD thin film deposition step, wherein plasma having directivity is applied in the second PEALD SiN thin film deposition step.
 13. The method of claim 12, wherein a nitrogen content of the second silicon nitride layer is greater than a nitrogen content of the first silicon nitride layer. 